Application of Gas-Expanded Liquids for Nanoparticle Processing: Experiment and Theory

Abstract

The numerous contributions to this ACS symposium series describe in detail the unique attributes of Gas eXpanded Liquids (GXLs) which provide for a novel class of solvents. Our contribution has applied GXLs as a processing medium for the fractionation and deposition of metallic nanoparticles (Pt, Pd, Ag, Au) and quantum dots (CdSe/ZnS). The tunable nature of the GXLs provides advantages over conventional solvents, and enables rapid, precise, and scalable size-dependant fractionation of nanoparticles into uniform populations (less than ± 0.5 nm in diameter). The wide range of accessible solvent strengths and facile removal of the CO 2 , substantially reduces the amount of solvent needed for conventional anti-solvent size fractionation techniques and facilitates solvent recycling. We have also taken advantage of the reduced surface tension and interfacial forces exhibited by GXLs to produce wide-area, low defect nanoparticle arrays. Each of these nanoparticle processing applications is governed by the inter-particle interactions; dispersive and steric repulsion forces, resulting from the solvation forces between the nanoparticle stabilizing ligands and CO 2 expanded liquid medium. To better understand this system, we have developed an interaction energy modeling approach to determine the interparticle attractive and repulsive forces that control nanoparticle dispersibility through variations in the properties of the GXL medium.